Despite the overall decline in the United States in the incidence of, and mortality from, gastric cancer, the rates of this disease among American rubber workers are significantly higher than expected, based on age-comparable U.S. data. Mortality data for rubber workers are based on standardized mortality ratios (SMR's) calculated for cohorts of employees, in several companies, identified in 1964 and followed for ten years. There exists rather convincing evidence from animal studies that certain environmental pollutants are capable of inducing gastric malignancies, and many of these agents are present in the industrial environment of the rubber industry. This epidemiologic study will use a case-control method, with four controls for each case, to determine if specific work area, or duration of employment (and hence potential exposure) is associated with the incidence of gastric cancer. The putative carcinogens under study are either fairly evenly distributed throughout the entire plant or are concentrated within specific work areas or jobs. The control selection procedure will enable us to determine which of these two possibilities is actually the case within the rubber industry. In addition, by matching on age, race, and sex, the possible confounding effects of these variables will be eliminated; statistical control of ethnicity and place of birth will be accomplished if these are found to differ between cases and controls.